CN102016089B - Brass alloy powder, brass alloy extruded material and method for producing the brass alloy extruded material - Google Patents

Abstract

A brass alloy powder having a brass composition consisting of a mixed phase of an α phase and a β phase, and containing 0.5 to 5.0% by mass of chromium. Chromium includes a component dissolved in the matrix of brass and a component precipitated at grain boundaries.

Description

Brass alloy powder, brass alloy extruded material and manufacturing method thereof

technical field

The invention relates to a high-strength brass alloy, in particular to a brass alloy powder and a brass alloy extruded material that do not contain lead harmful to the environment and human body.

Background technique

In recent years, environmental issues are looming, and attention to this aspect is necessary in alloy development. 6/4 brass has moderate strength and good mechanical properties, and is also non-magnetic, so it is used not only as mechanical parts, but also in a wide range of gas piping, water piping, and valves.

In order to improve the workability of members made of 6/4 brass, it is common to include a few percent of lead in the alloy composition. When this lead-containing brass member is used for water piping, lead may be leached into the water supply.

In order to solve the above problems, the development of lead-free brass raw materials has been carried out. As a conventional development example, there is a brass raw material to which bismuth is added instead of lead. A brass raw material in which a γ phase is precipitated, a brass raw material in which fine particles of silicon are dispersed, and the like. In these development technologies, it is necessary not only to achieve lead-free, but also to improve the strength of brass itself, and to expand the range of applications.

However, the current situation is that the addition of bismuth can only obtain the same level of strength as the addition of lead. Both bismuth and lead are elements that decrease the strength of brass by addition, and do not contribute to the improvement of the strength of brass members. The yield point, tensile strength, etc. Improvement, but the deformation ability of brass components is greatly reduced, and the workability is poor. In addition, there arises a problem in that the γ phase acts as a starting point for brittle fracture. The method of dispersing silicon particles contributes to the improvement of the mechanical strength of the brass alloy member, but has the disadvantage of degrading the machinability of the member.

In the 46th Copper and Copper Alloy Technology Research Conference Lecture Summary Collection (2006), pp.153-154, Kondo Katsuyoshi et al. "Characteristics of Machinable Brass Alloys" discloses a method for manufacturing a graphite particle-dispersed type machinable brass alloy based on powder metallurgy. The advantage of adding graphite is that it can be completely lead-free and that graphite floats on molten brass during recycling, so separation is easy. On the other hand, the added graphite cannot be expected to increase the strength of the brass member. Therefore, when graphite is added, the strength improvement technology of the brass member using the powder metallurgy method should also be considered.

Generally, if a low-melting-point metal is to be melted in a high-melting-point metal at high temperature, since the vapor pressure of the low-melting-point metal is high, the low-melting-point metal vaporizes rapidly during melting, and it is difficult to control the desired alloy composition.

Brass is an alloy of copper and zinc. If a refractory metal is added to this brass, it is possible to expect an improvement in strength. However, the boiling point of zinc is as low as 907°C, and it is difficult to add chromium with a melting point of 1907°C, vanadium with a melting point of 1902°C, and the like. If the temperature of the brass in the liquid phase state is increased, the evaporation amount of zinc will inevitably increase, and the alloy composition will rapidly change to the copper-rich direction.

As melting methods for high-melting point metals, there are electron beam melting methods, hydrogen plasma arc melting methods, etc., but these methods are not suitable for mass production and have been used for small-scale batch processing of rare metals. Also, these methods cannot prevent evaporation of low-melting metals.

A method of adding molten high-melting-point metal to low-melting-point metal is also conceivable, but heating and melting the high-melting-point metal to its melting point is industrially uneconomical in terms of cost, and mass production is difficult. Therefore, a method using the thermite reaction of oxides, a method of adding a master alloy with a lower melting point, and the like are generally performed.

JP-A-10-168533 (Patent Document 3) discloses a method of adding an alloy component to zinc. This gazette describes the use of a master alloy for the addition of chromium, but observation of the Zn-Cr thermal equilibrium state diagram reveals that chromium is hardly dissolved in zinc. In other words, it can be understood that Zn ₁₇ Cr or Zn ₁₃ Cr as a compound is dispersed in a zinc matrix. When this master alloy is added to zinc, only the composition ratio of zinc is increased, and the chromium compound is not changed. In this way, it is very difficult to dissolve a non-solid-solution element and a high-melting-point metal in a low-melting-point metal, and it is necessary to develop another method.

The addition of chromium to copper is an improvement over alloys containing zinc. Typical examples include the methods disclosed in JP-A-11-209835 (Patent Document 4) and JP-A-2006-124835 (Patent Document 5). In the methods disclosed in these gazettes, chromium, zirconium, tellurium, sulfur, iron, silicon, titanium, or phosphorus are contained in copper. Both are precipitation-type copper alloys, in which copper-zirconium compounds and the like are precipitated as strengthening phases, but unlike zinc-containing alloys, they can be alloyed even at high temperatures, which facilitates the production of these materials.

In the development of lead-free brass, it is known that the application of powder metallurgy is effective as a method of adding graphite. The main reason for this is that the mixing of graphite and brass is made possible by using powder. If the usual smelting method is used to try to add graphite, due to the different specific gravity of the two, the graphite floats on the brass metal solution and cannot be dispersed in the brass.

patent documents

Patent Document 1: JP-A-2000-309835

Patent Document 2: International Publication WO98/10106

Patent Document 3: Japanese Unexamined Patent Application Publication No. H10-168533

Patent Document 4: Japanese Unexamined Patent Publication No. H11-209835

Patent Document 5: JP-A-2006-124835

non-patent literature

Non-Patent Document 1: Summary of Lectures at the 46th Copper and Copper Alloy Technology Research Conference (2006), pp.153-154, Kondo Katsuyoshi, etc.

The inventors of the present application have been involved in the development of graphite-added brass as part of the development of lead-free brass alloys. However, the graphite particle-dispersed lead-free machinable brass alloy has the same strength as the lead-containing machinable brass alloy, and the strength is not significantly improved.

Contents of the invention

An object of the present invention is to provide a brass alloy powder that contributes to the improvement of the strength of a brass alloy member.

Another object of the present invention is to provide a brass alloy extruded material having excellent mechanical strength.

Still another object of the present invention is to provide a brass alloy member having excellent mechanical strength.

Still another object of the present invention is to provide a method of manufacturing a brass alloy extruded material having excellent mechanical strength.

The brass alloy powder according to the present invention has a brass composition consisting of a mixed phase of an α phase and a β phase, and contains 0.5 to 5.0% by mass of chromium. The above-mentioned chromium includes components dissolved in the matrix of brass and components precipitated at grain boundaries.

Extrusion processing of the aggregate of the above-mentioned brass alloy powder yields a brass alloy extruded material excellent in mechanical strength. In order to obtain desired mechanical strength, the chromium content must be 0.5% by mass or more. In order to further improve the mechanical strength of the finally obtained brass alloy extruded material, it is sufficient to increase the chromium content in the brass alloy powder, but from the viewpoint of current production, 5.0% by mass is the limit. A more preferable content of chromium is 1.0 to 2.4% by mass.

The chromium component that is forced into solid solution in the parent phase of brass suppresses the displacement movement in the crystallization and contributes to the improvement of the yield point. On the other hand, the chromium component precipitated at the grain boundary suppresses grain boundary sliding, causes extreme work hardening, and contributes to improvement of tensile strength. The solid-solution components in the parent phase of brass include components that are solid-solution-dispersed in the parent phase and components that are dispersed as precipitates in the parent phase.

At least one element selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, aluminum and tin may be contained in the brass alloy powder.

Preferably, the above-mentioned brass alloy powder is a rapidly solidified powder, more preferably, a powder rapidly solidified by a water spray method.

The brass alloy extruded material according to the present invention is obtained by extruding an aggregate of brass alloy powder having a brass composition consisting of a mixed phase of α phase and β phase and containing 0.5 ~5.0% by mass of chromium, the chromium includes components that are solid-solved in the parent phase of brass and components that precipitate at grain boundaries.

In one embodiment, the brass alloy extruded material has a 0.2% yield point of 300 MPa or more. In addition, the tensile strength is 500 MPa or more.

In order to improve the machinability of the brass alloy extruded material, in one embodiment, the brass alloy extruded material is mixed by adding 0.2 to 2.0% by weight of graphite particles to the brass alloy powder, and then the mixed powder is assembled obtained by extrusion. The particle size of the added graphite particles is preferably in the range of 1 μm to 100 μm.

The brass alloy member according to the present invention has a brass composition consisting of a mixed phase of α phase and β phase, and contains 0.5 to 5.0% by mass of chromium, and also contains a material selected from the group consisting of nickel, manganese, zirconium, vanadium, titanium, silicon, at least one of aluminum and tin. Chromium includes a component dissolved in the matrix of brass and a component precipitated at grain boundaries.

In order to improve the machinability of the brass alloy member, in one embodiment, the brass alloy member further contains graphite particles.

The manufacturing method of the brass alloy extruded material of the present invention comprises: the step of producing a brass alloy powder having a brass composition composed of a mixed phase of an α phase and a β phase and containing 0.5 to 5.0% by mass of chromium by a rapid solidification method , and the process of extruding the aggregate of the above-mentioned rapidly solidified brass alloy powder.

Preferably, the rapid solidification method is a water spray method. The heating temperature during extrusion processing is preferably 650° C. or lower.

The production method of one embodiment includes a step of adding 0.2 to 2.0% by weight of graphite particles to the brass alloy powder and mixing it before extrusion processing.

Including the items described above, the functions and effects brought about by the configuration of the present invention are described in detail in the following items.

Description of drawings

Fig. 1 is a SEM (scanning electron microscope) photograph showing the powder produced by the water spray method, (a) shows 6/4 brass alloy powder without Cr added, (b) shows 6/4 brass alloy powder added with 0.5% by mass Cr Brass alloy powder, (c) represents 6/4 brass alloy powder added with 1.0% by mass Cr.

Fig. 2 is a graph showing the X-ray diffraction results of the produced water spray powder.

Fig. 3 is a graph showing stress-strain curves of extruded materials.

Fig. 4 is a view showing a microstructure photograph of an extruded material obtained by an optical microscope, (a) showing an extruded material of a brass alloy green compact blank added with 1% by mass Cr, (b) showing an extruded material of a brass alloy green compact with 0.5% Cr added The extruded material of the brass alloy green compact billet, (c) shows the extruded material of the brass alloy green compact billet to which Cr is not added, and (d) shows the extruded material of the brass alloy smelted billet to which Cr is not added.

Fig. 5 is a photograph showing a SEM image of an extruded material of a brass alloy green compact material added with 1.0% by mass of Cr.

FIG. 6 is a graph showing the relationship between the concentration of solid-dissolved chromium components in the matrix of brass and the yield point.

Fig. 7 is a graph showing the relationship between the amount of graphite particles added and machinability.

Detailed ways

[New method of producing brass alloy powder]

The inventors of the present application studied a method of producing a high-strength machinable brass member that did not exist conventionally by increasing the strength of brass itself as a base material. As a method of increasing the strength of brass, a method of adding various additives is generally employed. For example, high-strength brass is a copper-zinc alloy with iron, aluminum, manganese, etc. added. It has a tensile strength of 460 MPa and excellent corrosion resistance, so it has been used in ship propellers and the like. However, the elongation of this high-strength brass is only guaranteed to be about 15%, and it cannot be said that the workability is good at all.

In order to develop an alloy focusing on the addition of graphite, it is necessary to produce a new type of brass alloy powder that has not existed until now, and to extrude the aggregate of this powder to improve the strength. Conventionally, the smelting method was used in the production of brass, but the present inventors attempted to produce a brass alloy having a new alloy composition by powder metallurgy instead of the smelting method.

According to the water spray method, which is one of the rapid cooling and solidification methods, the melt is rapidly cooled and solidified to produce powder, so that not only non-equilibrium phases appear in the powder, but also fine crystal grains are obtained. The present inventors made a new attempt by adding a small amount of chromium (Cr) as a third element to a brass alloy composed of a mixed phase of an α phase and a β phase to produce a powder having properties different from conventional brass powders. The aggregate of the powder was extruded and solidified by hot extrusion method, and a new material was obtained.

Attempts to improve the properties of brass by adding various additives have been carried out so far, but there is no precedent for actively adding transition elements to 6/4 brass by water spraying.

The present inventors proposed a new method for adding chromium as a refractory metal to 6/4 brass. As mentioned before, in order to melt the brass and dissolve the chromium into it, the molten soup must be heated to the melting point of chromium, but such heating temperature exceeds the boiling point of zinc. Therefore, in reality, it can be said that it is impossible to heat liquid brass up to the melting point of chromium, considering the high vapor pressure of zinc.

As another method for adding chromium to brass, the use of chromium-containing master alloys is considered. However, the copper-chromium master alloy also has a high melting point, and in the method of adding brass to the melted product, zinc still evaporates and cannot maintain a predetermined composition.

The present inventors have developed a brass alloy production method using a commercially available Cu-10%Cr master alloy. In the master alloy, chromium is dispersed as particles having a size of about 10 to 50 μm, and is not dissolved in copper. The master alloy is first melted at around 1200°C. At this temperature, the chromium contained in the master alloy does not melt, but floats in the liquid phase of copper in a solid state. In this state, copper is added, and adjustment is made so that the concentration of chromium becomes thinner. In this way, when the chromium concentration becomes about 4%, it exceeds the solid-liquidus line on the state diagram and becomes a single-phase state of the liquid phase. In this way, chromium, which is a refractory metal, can be brought into a mixed liquid phase with copper. Adding a predetermined amount of zinc in this state and performing rapid cooling and solidification by the water spray method can obtain a powder having a non-equilibrium phase in which chromium is forcibly dissolved in brass.

Vanadium can also be forced into solid solution in brass by the same method as above. However, in the binary state diagram of vanadium and copper, the solid-liquidus line is located at the position where the vanadium concentration is about 0.5%, so the amount of added vanadium becomes very small. Therefore, in reality, adding vanadium to brass is not only technically difficult, but also difficult to increase the effect of the addition.

According to the method developed by the present inventors, it is possible to appropriately control the composition of the alloy without evaporating the added zinc as much as possible. It is known that in 6/4 brass, the ratio of the α-phase and β-phase varies depending on the slight difference in the zinc component. In addition, it is also known that the difference in the ratio of α-phase and β-phase also affects the mechanical properties of brass alloys.

Therefore, from the viewpoint of composition control of brass alloys, it can also be seen that the above-mentioned powder generation method developed by the present inventors is an advantageous method for adding high-melting-point metals to brass. In addition, adding nickel and manganese which have a relatively low melting point will further increase the strength and improve the utility value of the obtained powder. In addition, when graphite is added to the thus obtained brass alloy powder and extruded, a lead-free machinable brass alloy excellent in strength and machinability can be obtained. As described above, the application range of the present invention is wide, so it can be said that the present inventors have opened the way to develop various types of lead-free brass having various mechanical properties.

The typical conventional method of refining grains is to repeatedly perform plastic working and heat treatment on a member. If powder metallurgy is used as in the present invention, a powder having a finer crystal structure is already prepared as a starting material. Therefore, No special process for miniaturization is required. In addition, the material composition has already been determined in the powder state, so the composition of the final product can be grasped at this stage. In addition to such superiority in the production process, the material according to the present invention has several excellent features described below.

[Effect added by third element]

In general, chromium hardly dissolves in brass. However, by employing a rapid solidification method such as a water spray method, only a certain amount of chromium dissolved in a liquid phase state is forcibly solid-dissolved in the brass matrix. In addition, along with crystal growth during solidification, a part of chromium aggregates at grain boundaries and precipitates as fine crystal grains. Strictly speaking, components dissolved in the matrix of brass include components dispersed in solid solution in the matrix and components dispersed in the matrix as precipitates. The chromium components forced into solid solution in the parent phase and the chromium components precipitated at the grain boundaries have different effects on the applied stress. That is, the chromium component that is forcibly dissolved in the parent phase suppresses the displacement movement in the crystal and contributes to the improvement of the yield point of the brass alloy member. On the other hand, the chromium component precipitated at the grain boundaries inhibits grain boundary sliding, causes extreme work hardening, and greatly contributes to the improvement of the tensile strength.

The effect when manganese is added is as follows. Unlike chromium, manganese basically dissolves in brass. Therefore, manganese does not generate grain boundary precipitates, does not cause extreme work hardening, and acts to increase both the yield point and the tensile strength in a balanced manner. The reason for this is considered to be that the manganese in solid solution in the parent phase restrains the displacement.

The effect when nickel is added is as follows. Nickel is also completely dissolved in brass, promotes the transformation from β phase to α phase during the hot extrusion process of brass alloy, forms a fine α phase in the crystal, and contributes greatly to the improvement of yield. However, nickel does not contribute to work hardening, so with regard to the maximum tensile stress, there is no big difference from the powder extrusion without nickel addition.

Chromium, manganese, and nickel are transition elements that appear in period 4 of the periodic table and, as mentioned above, have different effects when added to brass, showing completely different behavior. The reason is that each transition element strengthens brass by a different mechanism. Therefore, when two or more elements are added, it is considered that respective effects are exhibited.

In addition, the behavior when other elements are added can also be deduced from the above-mentioned research results. Vanadium, a transition element of period 4 of the periodic table, has an equilibrium diagram very similar to that of chromium. Therefore, if vanadium is added to make spray powder in the same way as chromium is added, there will be vanadium components that are forced into solid solution in the parent phase and vanadium components that precipitate at grain boundaries, and can improve the yellowing by the same strengthening mechanism as chromium. properties of copper.

In addition to the above-mentioned elements, titanium, silicon, aluminum, tin, etc., which are generally known as strengthening elements of brass, are also used as auxiliary additive elements, and are expected to effectively act on the strengthening of chromium-added brass.

[Quick cooling and solidification method]

The reason why the effects of the present invention are remarkably exhibited is that by producing brass alloy powder by the rapid solidification method, non-equilibrium phases and fine crystal grains are generated, and work hardening utilizing chromium grain boundary precipitation occurs. As an example of the rapid solidification method, the present inventors used a water spray method. The water spray powder of 6/4 brass composition is characterized by a β phase which becomes a non-equilibrium phase. To be more specific. In the rapid solidification process of 6/4 brass alloy, the position beyond the solid-liquidus line is the β-phase region, so the powder solidifies as β-phase. If it is slowly cooled as it is, the phase transition should proceed to a mixed phase of the α phase and the β phase, but this phase transition hardly occurs due to the high degree of rapid cooling. When the temperature is raised during thermal processing of the β-phase powder, a phase transition from the β-phase to the α-phase occurs to form a mixed phase.

A certain additive element exerts the effect of stably maintaining the β phase. The effect of delaying the transition to the α phase was confirmed for chromium and manganese. This is considered to be the effect of suppressing the diffusion of atoms in the crystal grains, and the effect of maintaining the non-equilibrium phase formed by rapid solidification is high.

In the present invention, grain boundary sliding is suppressed by grain boundary precipitates during solidification, and the work hardening phenomenon is remarkably manifested. Preferably, the size of the grain boundary precipitates is controlled to a size (maximum length) of about 100 nm to 500 nm. In addition, the dispersion state of the precipitate is also an important factor, and it is ideal that the precipitate is uniformly dispersed in the structure, so it is desirable that the raw material powder be homogeneous. As a powder production method, if it is a spray method, it is easy to control the coagulation rate and the accompanying powder particle size.

[extrusion processing]

The extrusion temperature becomes a very important factor for the improvement of the strength of the brass alloy extruded material. The lower the extrusion temperature, the better. In order to extrude an aggregate of powders, it is necessary to heat the powders. If the heating temperature is high, atomic diffusion is accelerated, and the non-equilibrium phase produced by rapid solidification approaches a state of thermal equilibrium. Therefore, it is important to extrude the brass alloy powder aggregate at the lowest temperature at which extrusion processing can be performed. The preferred extrusion temperature is below 650°C. It is difficult to determine the lower limit value of the extrusion temperature. The reason is that the lower limit temperature is determined by the size of the extruded billet, the extrusion ratio, the maximum extrusion load of the device, and the like. If extrusion is possible at 500°C, this temperature can be said to be an appropriate condition, but actually, it is considered that 550°C or higher is necessary for extrusion processing.

During extrusion, the actual extrusion temperature is determined by two factors, the temperature drop due to the exothermic heat of the billet and the temperature rise caused by the extrusion pressure. Therefore, it is unrealistic to specify the extrusion temperature, and it is practical to manage the heating temperature of the billet. In the extrusion experiment of brass, when the heating management temperature of the billet was set to 650° C., it took 48 seconds until extrusion started. Referring to the data obtained in the simulation experiment, the extrusion start temperature at this time was 577°C.

The inventors of the present invention have found that a higher strength material can be obtained by controlling the extrusion speed when extruding a chromium-containing brass alloy powder aggregate. Extrusion at low temperature is effective as an extrusion condition for obtaining a material with higher strength, and further improvement in strength can be expected by lowering the extrusion speed. This point will be described later based on experimental results.

In order to improve the machinability of the brass alloy extruded material, graphite particles may be added and mixed to the chromium-containing brass alloy powder, and the mixed powder assembly may be extruded. In order to exhibit the effect of improving machinability, it is necessary to add 0.2 to 2.0% by weight of graphite particles to the brass alloy powder containing chromium. The particle size of the added graphite particles is preferably within a range of 1 μm to 100 μm.

[Amount of element added]

Regarding the amount of the third element added, each element has its own suitable amount.

With regard to chromium, an improvement in the yield point was confirmed with the addition of 0.5% by mass. When the amount of chromium added was further increased to 1% by mass, no difference was found in the yield point, but the tensile strength showed a very high value. Therefore, the amount of chromium added is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more.

The upper limit of the chromium content is 5.0% by mass. The upper limit of the concentration of chromium in the copper-chromium liquid phase state becomes 4% due to the limitation of the powder manufacturing stage. However, when zinc was added, the chromium content was 2.4% by mass. The content of chromium can be increased by increasing the melting temperature of copper-chromium. For example, if the melting temperature is raised to 1300° C., chromium can be melted to a concentration of 8%, and the chromium content when zinc is added becomes 5.0% by mass. However, at this temperature, the vapor pressure of zinc increases excessively, and composition control becomes difficult. Therefore, a more preferable upper limit of the chromium content is 2.4% by mass.

Even an extremely small amount of vanadium causes grain boundary precipitation. Considering that the upper limit of the concentration of vanadium in the copper-vanadium liquid phase state is 0.5%, vanadium should be added near the upper limit in order to maximize the effect of vanadium. In this case, the concentration of vanadium becomes 0.3% by mass due to the addition of zinc. In order to make the concentration of vanadium larger than this value, the melting temperature must be raised. However, at a temperature of 1200° C. or higher, the vapor pressure of zinc becomes excessively high, making it difficult to produce a powder with an optimum composition. Therefore, there is a limit to the effect of adding vanadium, and strengthening in combination with other elements is required.

There are many research examples on the effect obtained by adding manganese to brass, and it has also been put into practical use as high-manganese brass. In the present invention, it is possible to further increase the strength of the brass alloy by adding manganese in combination with the above-mentioned addition of chromium or the addition of chromium and vanadium. As the amount of manganese added, it was confirmed that a sufficient effect can be obtained at 0.5% by mass. According to previous research examples, it has also been confirmed that increasing the amount of manganese added significantly reduces the workability of the material. Therefore, the preferable upper limit of the added amount of manganese is the range where no compound can be produced, that is, 7% by mass or less. A more preferable amount of manganese to be added is 1 to 3% by mass. If the amount exceeds this amount, the elongation may decrease, leading to a decrease in brass workability.

Nickel has an infinite solid solution to copper, and can be alloyed by adding an arbitrary amount to the Cu-Zn-Ni system. Therefore, in the present invention, there is no particular upper limit to the amount of nickel added. The addition of nickel has a special effect of only increasing the yield point, and the addition of 1% by mass can achieve a yield point exceeding 300 MPa.

From a practical viewpoint of an alloy member, it goes without saying that the yield point is more important than the tensile strength. The greatest effect of the present invention is to include a predetermined amount of chromium in 6/4 brass, but more advantages can be obtained by further adding nickel. Chromium has a high melting point, so it is not easy to add even a small amount. As a method of overcoming this, a method of utilizing a metallurgical heat equilibrium state has been described. In order for the effects of chromium and nickel to appear at the same time, these two elements must of course be added. As an addition method in this case, there is an easier method. That is, if only chromium is to be added, the aforementioned process is adopted, but if nickel is also to be added at the same time, it is preferable that chromium and nickel are contained in the master alloy from the beginning.

Nickel-chromium alloys are commercially available, and their melting point drops to 1345°C through alloying. This alloy can be melted with copper using a high frequency furnace. The mixing ratio of nickel and chromium is 1:1, and it is very easy to make a molten soup compared with the production using a copper-chromium master alloy. When nickel is added using this method, the preferable upper limit of the amount of nickel added is 2.4% by mass, which is the same as that of chromium.

The amount of nickel added can be increased by changing the mixing ratio of nickel and chromium in the master alloy. Increasing the amount of chromium added to the master alloy can sharply increase the melting point, so powder production becomes more difficult, but even if the ratio of nickel is increased, the melting point does not rise too much and does not exceed the melting point of nickel. Therefore, nickel-rich powder can be produced, and the addition amount of nickel can be increased. The upper limit of the amount of nickel added is not particularly limited, but it is desirable to add 5% by mass or less as a range that does not impair the properties of brass. If the content of nickel is within this range, an alloy having desired mechanical properties can be produced, and it can be used in a wide range of applications.

As for other added elements, it is about a few percent, at least 0.1% or more, so that the added effect appears. The appropriate amount and combination of various elements vary according to the required mechanical properties. From the point of view of improving strength, zirconium exhibits a crystal grain refining effect, and its effect can be fully confirmed even when added at 0.1%, and it can be said to be a clear strengthening element based on Hall-Petch's empirical law.

Titanium, aluminum, and the like increase the strength of the parent phase by solid solution strengthening, and even a trace amount of 1% or less can exhibit this effect.

Silicon is usually an element used for dispersion strengthening, and an addition of about 3% is an appropriate amount. However, from the perspective of taking into account other elements, sometimes adding does not necessarily lead to strengthening. In particular, in the alloy system of the present invention, if the chromium precipitation site and the silicon dispersion site are at the same position, the strengthening effect cannot be obtained. Therefore, the amount of silicon added is limited by the amount of chromium added, and the total of chromium and silicon is preferably 3% or less.

Tin is in solid solution at about 0.3% and exhibits the effect as a strengthening element. If the added amount is increased, the γ phase will appear, which will cause embrittlement. It is not suitable to add a large amount, and the range of 0.1% to 0.5% is suitable.

[production of powder]

Brass powder without Cr addition, brass powder with 0.5% by mass Cr addition, and brass powder with 1.0% by mass Cr addition were produced from Cu-40%Zn brass raw material by water spray method. The chemical composition of the powder is shown in Table 1, and the SEM (scanning electron microscope) photograph of the appearance of the powder is shown in FIG. 1 . (a) of Fig. 1 shows 6/4 brass alloy powder without adding Cr, (b) shows 6/4 brass alloy powder with 0.5% by mass Cr added, and (c) shows 6/4 brass alloy powder with 1.0% by mass Cr added. /4 brass alloy powder.

[Table 1]

Chemical Composition of Powder

The results of X-ray diffraction of the produced powder are shown in FIG. 2 . For the brass alloy powder to which Cr was not added and the brass alloy powder to which 0.5% by mass of Cr was added, only the β phase was detected. In the brass alloy powder to which 1.0% by mass of Cr was added, two phases, the α phase and the β phase, were detected. In the case of 6/4 brass composition, if the liquid phase exceeds the solid-liquidus line, it becomes a β phase, and the rapidly solidified powder is generally cooled without an α phase transition. A detailed investigation of the brass alloy powder to which 1.0% by mass of Cr was added revealed a mixed state of α-phase powder and β-phase powder. It is considered that a difference in cooling rate occurs among the individual powders during the spraying process, and an α-phase-transformed powder is produced. In addition, since Cr exists as fine particles, no clear diffraction peak is detected in X-ray diffraction.

[Extrusion of 1.0% by mass Cr-added brass alloy powder]

The powder with the composition of 59%Cu-40%Zn-1%Cr produced by the water spray method is compressed under 600Mpa to make a billet for extrusion. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

A tensile test piece with a gauge length of 10 mm and a girth of 3 mm was cut out from the bar, and subjected to a tensile test to measure the 0.2% yield point and maximum tensile strength. The results are shown in Table 2.

[Table 2]

Add 1% Cr brass alloy extrusion material

Heating temperature Maximum tensile strength 0.2% yield point 650℃ 565MPa 317MPa 700℃ 556MPa 319MPa 750℃ 547MPa 289MPa 780°C 544MPa 294MPa

As can be seen from the results in Table 2, the product extruded by heating the billet to a temperature of 650° C. showed high values in terms of maximum tensile strength and 0.2% yield point. If the heating temperature is increased, their mechanical strength tends to decrease. Therefore, the heating temperature of the billet before extrusion is preferably 650° C. or lower.

[Extrusion of brass alloy powder with 0.5% by mass Cr added]

The powder with the composition 59.5%Cu-40%Zn-0.5%Cr produced by the water spraying method is pressed at 600Mpa to make a billet for extrusion. This billet was heated in an electric furnace and extruded. The temperature conditions of the electric furnace for heating were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

A tensile test piece with a gauge length of 10 mm and a girth of 3 mm was cut out from the bar, and subjected to a tensile test to measure the 0.2% yield point and maximum tensile strength. The results are shown in Table 3.

[table 3]

Add 0.5% Cr brass alloy extrusion material

Heating temperature Maximum tensile strength 0.2% yield point 650℃ 524MPa 317MPa 700℃ 514MPa 297MPa 750℃ 516MPa 287MPa 780°C 514MPa 298MPa

As can be seen from the results in Table 3, the product extruded by heating the billet to a temperature of 650° C. showed high values in terms of maximum tensile strength and 0.2% yield point. These mechanical strengths tend to decrease if the heating temperature is increased. Therefore, the heating temperature of the billet before extrusion is preferably 650° C. or lower.

In addition, as compared with the results in Table 2, it can be seen that the product added with 0.5% Cr and the product added with 1.0% Cr showed substantially the same value with respect to the 0.2% yield point. Therefore, it was confirmed that the yield point was maintained even if the amount of chromium added was small. However, if the amount of chromium is reduced, the maximum tensile strength is reduced. This supports the fact that the yield point is determined by the amount of chromium that is forced into solid solution, while the maximum tensile stress is increased by work hardening due to the precipitation of the remaining chromium at the grain boundaries.

[Extrusion of brass alloy powder with 1.0% by mass Ni added]

The powder with composition 59%Cu-40%Zn-1.0%Ni produced by water spraying method was compressed under 600MPa to make a billet for extrusion. Extrusion processing is carried out by heating this billet with an electric furnace. The temperature conditions of the electric furnace for heating were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

A tensile test piece with a gauge length of 10 mm and a girth of 3 mm was cut out from the bar, and subjected to a tensile test to measure the 0.2% yield point and maximum tensile strength. As a result, the product extruded by heating the billet at 650° C. had a 0.2% yield point of 311 MPa and a maximum tensile strength of 479 MPa. These mechanical strengths tend to decrease if the heating temperature is increased. Therefore, the heating temperature of the billet before extrusion is preferably 650° C. or lower.

[Extrusion of brass alloy powder with 0.7 mass% Mn added]

The powder with composition 59%Cu-40%Zn-0.7%%Mn prepared by water spraying method is compressed under 600MPa to make a billet for extrusion. This billet is heated in an electric furnace for extrusion processing. The temperature conditions of the electric furnace for heating were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

Tensile test pieces of 10 mm and girth of 3 mm were cut out from the rods, subjected to a tensile test, and the 0.2% yield point and maximum tensile strength were measured. As a result, the product extruded by heating the billet at 650° C. had a 0.2% yield point of 291 MPa and a maximum tensile strength of 503 MPa. If the heating temperature is increased, the mechanical strength of these tends to decrease. Therefore, the heating temperature of the billet before extrusion is preferably 650° C. or lower.

[Extrusion of Cr-free brass alloy powder]

The powder with the composition of 60% Cu-40% Zn produced by the water spraying method is compressed under 600 MPa to make a billet for extrusion. This billet is heated in an electric furnace for extrusion processing. The temperature conditions of the electric furnace for heating were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

A tensile test piece with a gauge length of 10 mm and a girth of 3 mm was cut out from the bar, and subjected to a tensile test to measure the 0.2% yield point and maximum tensile strength. The results are shown in Table 4.

[Table 4]

Brass Alloy Extrusion Material Without Added Cr

Heating temperature Maximum tensile strength 0.2% yield point 650℃ 466MPa 273MPa 700℃ 460MPa 259MPa 750℃ 471MPa 263MPa 780°C 450MPa 234MPa

As can be seen from the results in Table 4, the product extruded by heating the billet to a temperature of 650° C. showed high values in terms of maximum tensile strength and 0.2% yield point. If the heating temperature is increased, their mechanical strength tends to decrease. Therefore, the heating temperature of the billet before extrusion is preferably 650° C. or lower.

[Extrusion of smelted billet of brass alloy without Cr addition]

The smelted material ingot with the composition of 60% Cu-40% Zn is heated in an electric furnace for extrusion processing. The temperature conditions of the electric heating furnace were set to four types of 650°C, 700°C, 750°C, and 780°C. The billet was processed by an extruder under conditions of an extrusion speed of 3 mm/s and an extrusion ratio of 37 to obtain a rod.

A tensile test piece having a gauge length of 10 mm and a girth of 3 mm was cut out from the bar, and subjected to a tensile test. As a result, the product extruded by heating the billet at 650° C. had a 0.2% yield point of 226 MPa and a maximum tensile strength of 442 MPa.

[Comparison of maximum tensile strength and 0.2% yield point]

Table 5 compares the maximum tensile strength and 0.2% proof point of extruded brass alloy materials obtained by heating various billets to a temperature of 650° C. and extruding them. In addition, the stress-strain curve of the extruded material is shown in FIG. 3 . The blanks to be compared were smelted blanks of brass alloys without Cr addition, brass alloy compact blanks without Cr addition, brass alloy compact blanks with 0.5% Cr addition, and brass alloy compact blanks with 1.0% Cr addition. There are 4 kinds of powder blanks.

[table 5]

Comparison of the strength of billets made of various brass alloys (heated and extruded at 650°C)

The type of billet Maximum tensile strength 0.2% yield point Smelted billets without Cr added 442MPa 226MPa Pressed powder blank without adding Cr 466MPa 273MPa Add 0.5% Cr to the green compact 524MPa 317MPa Added 1.0% Cr green compact 565MPa 317MPa

From FIG. 3 and Table 5, the following can be understood. First, comparing two types of brass alloy billets to which Cr was not added, the green compact billets showed higher values in both the maximum tensile strength and the 0.2% yield point than the melted billets. Specifically, the maximum tensile strength was increased by 5.4% and the 0.2% proof point was increased by 20.7% by using green compact. Only from this aspect, the superiority of the powder metallurgy method is obvious.

Furthermore, comparing the green compact billet to which 1.0 mass % of chromium was added and the smelted billet to which Cr was not added, the maximum tensile strength of the extruded material of the green compact billet to which 1.0 mass % of Cr was added was increased by 27.8 %, 0.2% yield point increased by 40.2%. The 0.2% yield point is greatly increased, which is considered to be the solid solution strengthening caused by the forced solid solution of chromium.

In addition, it was confirmed that the maximum tensile strength of the green compact green sheet to which Cr was added was greatly improved as compared with the green compact green sheet to which Cr was not added. The reason for this is believed to be that during the solidification process of the powder manufacturing process, chromium that is not completely solid-dissolved is concentrated at the grain boundary, resulting in grain boundary segregation of chromium, and spherical precipitates with a diameter of about 100nm to 500nm mainly exist in the grains Boundary triple point, grain boundary. Such fine precipitates act as a large resistance against grain boundary sliding during plastic deformation, and as a result, exhibit a high degree of work hardening.

[organizational observations]

FIG. 4 shows the observation results of the structure of the extruded material extruded with the heating temperature of the billet at 650° C. by an optical microscope. (a) of FIG. 4 shows the extruded material of the brass alloy green compact billet added with 1 mass % Cr, (b) shows the extruded material of the brass alloy green compact billet added with 0.5 mass % Cr, and (c) The extruded material of the Cr-free brass alloy compact billet is shown, and (d) shows the extruded material of the Cr-free brass alloy melting billet.

Comparing the photographs in Fig. 4 shows that the green compact extruded material has finer grains than the extruded material of the smelted billet. In the case of brass alloy smelted billet extruded material, the grain size was 3 to 10 μm, but the crystal grain size of the brass alloy compact billet extruded material without adding Cr was finer and 1 to 6 μm. In addition, when used as a Cr-added brass alloy green compact extrusion material, it was confirmed that the crystal grain size was further refined, and it was submicron to 5 μm.

As the grain size becomes smaller, the yield point increases according to Hall-Petch's empirical rule. In the structure of the Cr-added material, black dot-like fine precipitates of 1 μm or less were observed at the grain boundaries. As a result of EDS analysis, these precipitates were identified as Cr.

FIG. 5 shows a SEM image of an extruded material of a brass alloy green compact material added with 1% by mass of Cr.

In addition, in the above description, the brass alloy powder or the brass alloy powder extruded material was mainly described, but this invention is applicable also to a brass alloy member. That is, the brass alloy member has a brass composition consisting of a mixed phase of α phase and β phase, contains 0.5 to 5.0% by mass of chromium, and further contains At least one element of .

[Increase in Yield Stress (YS)]

It was confirmed that the addition of chromium increases the yield stress of the brass alloy member, but what contributes to this increase in yield stress is the chromium component in chromium, especially the chromium component dispersed in solid solution in the matrix of brass. The precipitates were quantified using the results of the microstructure analysis, and the amount of chromium solid-dissolved in the matrix was calculated from the amount of added chromium.

In FIG. 6, the difference between the yield stress of the brass alloy member without chromium added and the brass alloy member added with chromium is shown on the vertical axis, and the concentration (%) of the solid-dissolved chromium component in the parent phase is shown on the horizontal axis. axis. When the chromium solid solution is 0.22%, the increase of yield stress is 34MPa, and when the chromium solid solution is 0.35%, the increase of yield stress is 54MPa. Thus, it was confirmed that the yield stress increases in proportion to the concentration of solid-dissolved chromium in the parent phase of brass.

[Improvement of machinability by adding graphite particles]

In the manufacture of brass alloy extruded materials using powder extrusion, by adding graphite particles, it can become lead-free and suppress adverse effects on the environment. Adding graphite to general brass has been done in the past, but there is no precedent for adding graphite to brass alloys whose strength is improved by adding chromium. Therefore, an attempt was made to improve machinability by adding graphite to brass whose strength was improved by adding chromium.

The average particle diameter of the graphite particles used was 5 μm. The chromium-containing brass powder produced by the water spray method was mixed with graphite particles by mechanical stirring. This mixed powder was made into a green compact in the same manner as the above-mentioned method, and subjected to hot extrusion processing to obtain a rod. The amount of graphite particles to be added was three types of 0.5% by weight, 0.75% by weight, and 1.0% by weight relative to the chromium-containing brass alloy powder.

Fig. 7 is a graph showing the relationship between the amount of graphite particles added and machinability. When graphite particles were added to chromium-containing brass alloy powder and extruded, it was found that machinability was significantly improved. Machinability was evaluated by measuring the test time of a penetration test using a drill. The test piece was cut into a round bar with a length of 5 cm, and a penetration test was performed with a drill bit diameter of 4.5 mm. A load of 1.3 kgf was applied to the drill, and the number of revolutions of the main shaft was 900 rpm. Ten tests were performed, and the average value of the time required for penetration is shown in the graph of FIG. 7 .

In the test piece to which graphite was not added at all, the drill did not penetrate completely even if the cutting was performed for 180 seconds or longer. Since the cutting of the drill bit was seen to be stopped, the test was terminated here for the case where there was no penetration in 180 seconds.

Investigate the relationship between the amount of graphite added and the time required for drill penetration. For a brass alloy containing 0.5% of chromium, it took 180 seconds or more without adding graphite, and it took an average of 28 seconds for the drill to penetrate in the case of adding 0.5% of graphite. When the amount of graphite added is 0.75% or more, the penetration time becomes 20 seconds or less, and a significant improvement in machinability was confirmed. Therefore, in the case of a brass alloy containing 0.5% of chromium, the addition of 0.75% or more of graphite can be said to be a suitable condition for greatly improving machinability.

For a brass alloy containing 1.0% chromium, even if 0.5% graphite is added, the penetration time is 180 seconds or more. If the graphite addition was increased to 0.75%, it took an average of 38 seconds for the drill to penetrate. Also, when the amount of graphite added is 1.0%, the penetration time becomes 20 seconds or less. Therefore, in the case of a brass alloy containing 1.0% of chromium, the addition of 1.0% or more of graphite can be said to be a suitable condition for greatly improving machinability.

[Increase in strength due to low-speed extrusion]

The present inventors have found that by controlling the extrusion speed of a brass alloy containing chromium, a higher strength material is obtained. Extrusion at a low temperature is effective as an extrusion condition for obtaining a high-strength material, and the strength can be further increased by further reducing the extrusion speed. If the measured value is described, in the case of a brass alloy containing 1.0% chromium, the yield point when extruded at a normal extrusion speed (ram speed (ram speed) 3mm/s) is 317MPa, and the maximum tensile The strength was 565Mpa, but the extrusion speed was reduced to one-tenth (slider speed 0.3mm/s) for extrusion processing. As a result, the yield point increased to 467Mpa and the maximum tensile strength increased to 632MPa.

The embodiments of the present invention have been described above with reference to the drawings, but the present invention is not limited to the illustrated embodiments. Various modifications and variations can be added to the illustrated embodiments within the same or equivalent range as the present invention.

The present invention can be advantageously utilized in the manufacture of 6/4 brass alloy components with excellent mechanical properties.

Claims (15)

1. brass alloys powder is to have by α mutually and the brass alloys powder formed of the brass of β mixing phase composition mutually, and it contains the chromium of 0.5～5.0 quality %, and above-mentioned chromium is included in the composition of solid solution in the parent phase of brass and the composition of separating out at crystal boundary.

2. brass alloys powder as claimed in claim 1, wherein the composition of solid solution is included in composition that solid solution disperses in the parent phase and the composition that in parent phase, disperses as precipitate in the parent phase of above-mentioned brass.

3. brass alloys powder as claimed in claim 1, wherein the content of above-mentioned chromium is 1.0～2.4 quality %.

4. brass alloys powder as claimed in claim 1 wherein comprises at least a element that is selected from nickel, manganese, zirconium, vanadium, titanium, silicon, aluminium and the tin in above-mentioned powder.

5. brass alloys powder as claimed in claim 1, wherein above-mentioned powder is the quench solidification powder.

6. brass alloys powder as claimed in claim 5, wherein above-mentioned quench solidification powder are the powder that adopts water spray method quench solidification.

7. brass alloys extruded material; It obtains through the aggregate of the brass alloys powder that is described below being extruded processing; This brass alloys powder have by α mutually and the brass of β mixing phase composition mutually form and contain the chromium of 0.5～5.0 quality %, above-mentioned chromium is included in the composition of solid solution in the parent phase of brass and the composition of separating out at crystal boundary.

8. brass alloys extruded material as claimed in claim 7, its 0.2% yield point is more than the 300MPa.

9. brass alloys extruded material as claimed in claim 7, its hot strength are more than the 500MPa.

10. brass alloys extruded material as claimed in claim 7, it is through after adding the graphite particle of 0.2～2.0 weight % and mixing to above-mentioned brass alloys powder, this mixed-powder aggregate is extruded processing and obtained.

11. brass alloys extruded material as claimed in claim 10, the particle diameter of wherein above-mentioned interpolation graphite particle is in the scope of 1 μ m～100 μ m.

12. the manufacturing approach of a brass alloys extruded material comprises:

Adopt emergency cooling solidification method to make to have by α mutually and the brass of β mixing phase composition mutually form and contain 0.5～5.0 quality % chromium the brass alloys powder operation and

Aggregate to the brass alloys powder of above-mentioned quench solidification is extruded the operation of processing.

13. the manufacturing approach of brass alloys extruded material as claimed in claim 12, wherein above-mentioned emergency cooling solidification method is the water spray method.

14. the manufacturing approach of brass alloys extruded material as claimed in claim 12, the wherein above-mentioned heating-up temperature that adds man-hour of extruding is below 650 ℃.

15. the manufacturing approach of brass alloys extruded material as claimed in claim 12, above-mentioned extrude processing before, have the operation of above-mentioned brass alloys powder being added the graphite particle that mixes 0.2～2.0 weight %.

Images